As strange as it is to see a horse on the road, it is even more strange to see the rider not-riding. So it is a common question asked of me "Why are you walking? Don't you ride?"
Yes, I do ride Apollo (see?).
But I also walk. A lot. This is for many reasons, and sometimes several reasons at once.
Sometimes the question is rephrased as "Is your horse ok?" because one of the more typical reasons to not-ride is if your horse has become injured. In my case, I sometimes choose to walk to prevent injury. Both for Apollo and for myself. On a 10,000 mile journey, his back and my legs can get sore if I stay mounted for too many hours. Me walking gives him a break and also gives my muscles and joints a chance to move and stretch differently.
Another major reason I walk is for safety. If we are traveling along a busy road, or a road with a fast speed limit, or a road with no shoulder (in other words, no margin of error to stay away from traffic), or in a situation where me falling off would be particularly dangerous (such as on a bridge) or where Apollo is likely to get frightened (such as near a train), we are both safer if I am walking. This gives me better leverage if he suddenly moves or tries to run, and keeps me from falling into traffic (or over the side of a bridge). It also helps me keep Apollo safe from suddenly moving in a dangerous direction because he is more likely to follow me when I'm walking, and it is quicker and more effective for me to correct him if he starts to go the wrong way when I am standing next to him.
Some days I have to walk all day or nearly all day, some days I can ride as much as is physically comfortable for the both of us. It depends on where we are and how Apollo is feeling.